This invention relates to a process for producting an integral skin polyurethane foam.
Integral skin polyurethane foams produced by mixing an isocyanate, a polyether having active hydrogen, a blowing agent, a catalyst and the like, and conducting foaming and curing in a closed mold are excellent in thermal insulation, sound absorption, and strength, so that they are suitable for use as electric machinery and appliances, materials for electronic parts, building materials, etc. With recent development in reaction injection molding technique, applications of these foams are increasing remarkably. But one factor which restricts industrial applications of foamed polyurethane products is that the molding cycle is long, particularly the removal time of a foamed product from a mold (i.e., a time required for injecting the composition into the mold and taking out the foamed product from the mold) is long. That is to say, when a foamed product is taken out of a mold in a short time, there take place peeling of the skin, blister of the foam, generation of small voids on the surface, and the like, so that the molded material should be maintained in the mold for a long time compared with injection molding of thermoplastic resins.
In order to shorten the removal time of the foamed products from the mold, there have been proposed various processes such as increasing the amount of a catalyst, using a catalyst having high activity, raising the liquid temperature, and the like, but these processes also had disadvantages such as the flowability of the foam being lowered, surface properties of the foam becoming worse, and the like.